In tough times, mom makes hornier sons

A new study shows that female dung beetles can control the size of their son's horns, a critical morphological feature that allows its male offspring to succeed in the fight for a female.
The study, led by Bruno Buzatto, from the University of Western Australia and published online on July 23 in the journal BMC Evolutionary Biology, is the first to show such a maternal effect in dung beetles.

Maternal effects occur when environmental factors influence the expression of genes in the mother, which then have an effect on particular features of her offspring. These maternal effects are expected to evolve whenever females have more data, compared to their young, of the environmental conditions they will experience after birth. By affecting their young, females can help ensure a better chance for development, reproduction, and ultimately, survival, for their offspring.

In dung beetles, Onthophagus taurus, one successful way to mate and guard females is to fight, and to be a good fighter you need big horns. In this study, researchers set out to answer the question of whether female dung beetles were capable of perceiving population density, and responding accordingly by changing the horn size of their male offspring.

The researchers reared female dung beetles in isolation, and other females in a crowded setting, and they then studied how their offspring were affected.
"We found that mothers who were reared with other conspecifics (members of the same species) before their mating period produced offspring that had longer horns across a wider range of body sizes than the offspring of females that were reared in isolation before their mating period," said the researchers.

Their results show a novel behaviour that allows female dung beetles to produce better-equipped sons, which will likely allow them to succeed in the important task of sexual competition.

Original Article: Maternal effects on male weaponry: female dung beetles produce major sons with longer horns when they perceive higher population density